Thermal performance of a parabolic trough collector with a longitudinal externally finned absorber

A new absorber configuration has been proposed for parabolic trough solar collector. It consists of a tube through which the working fluid flows. The tube is attached externally to two longitudinal fins which are directed normally to the collector aperture. The absorber aggregate, tube and fins, is encased by a transparent envelope. The heat balance equations for such absorber have been derived and solved. Based on these analyses a study has been carried out on an absorber located in Alexandria (31^o N latitude) in Egypt to show the effect of its geometrical parameters on the thermal performance. The results of the study show that a wide range of concentration ratios, higher than the smallest ideal ones, can be chosen. For each concentration ratio, there is a corresponding fin height to absorber tube diameter ratio which maximizes the collector efficiency. The greatest collector efficiency is achieved when the concentration ratio is 1.7 of the smallest ideal one and the ratio of fin height to tube diameter in 0.7. In this case the collector efficiency increases in average ca. 3% over that when using a conventional absorber.     

Pesticide Residues in Vegetables and Fruits from Farmer Markets and Associated Dietary Risks

The use of pesticides leads to an increase in agricultural production but also causes harmful effects on human health when excessively used. For safe consumption, pesticide residues should be below the maximum residual limits (MRLs). In this study, the residual levels of pesticides in vegetables and fruits collected from farmers’ markets in Sharkia Governorate, Egypt were investigated using LC-MS/MS and GC-MS/MS. A total number of 40 pesticides were detected in the tested vegetable and fruit samples. Insecticides were the highest group in detection frequency with 85% and 69% appearance in vegetables and fruits, respectively. Cucumber and apple samples were found to have the highest number of pesticide residues. The mean residue levels ranged from 7 to 951 µg kg⁻¹ (in vegetable samples) and from 8 to 775 µg kg⁻¹ (in fruit samples). It was found that 35 (40.7%) out of 86 pesticide residues detected in vegetables and 35 (38.9%) out of 90 pesticide residues detected in fruits exceeded MRLs. Results for lambda-cyhalothrin, fipronil, dimothoate, and omethoate in spinach, zucchini, kaki, and strawberry, respectively, can cause acute or chronic risks when consumed at 0.1 and 0.2 kg day⁻¹. Therefore, it is necessary for food safety and security to continuously monitor pesticide residues in fruits and vegetables in markets.     

Design,Synthesis, Anticancer Activity and Molecular Docking of New 1,2,3-Triazole-Based Glycosides Bearing 1,3,4-Thiadiazolyl,Indolyl and Arylacetamide Scaffolds

New 1,3,4-thiadiazole thioglycosides linked to a substituted arylidine system were synthesized via heterocyclization via click 1,3-dipolar cycloaddition. The click strategy was used for the synthesis of new 1,3,4-thiadiazole and 1,2,3-triazole hybrid glycoside-based indolyl systems as novel hybrid molecules by reacting azide derivatives with the corresponding acetylated glycosyl terminal acetylenes. The cytotoxic activities of the compounds were studied against HCT-116 (human colorectal carcinoma) and MCF-7 (human breast adenocarcinoma) cell lines using the MTT assay. The results showed that the key thiadiazolethione compounds, the triazole glycosides linked to p-methoxyarylidine derivatives and the free hydroxyl glycoside had potent activity comparable to the reference drug, doxorubicin, against MCF-7 human cancer cells. Docking simulation studies were performed to check the binding patterns of the synthesized compounds. Enzyme inhibition assay studies were also conducted for the epidermal growth factor receptor (EGFR), and the results explained the activity of a number of derivatives.     

Recent developments of derivative spectrophotometry and their analytical applications.

Articles about the development of derivative spectrophotometric methods and analytical applications of derivative spectrophotometry (DS) published in the last nine years (since 1994) are reviewed.     

Microstructure dependence of yielding and fracture in Cd-Zn alloys

The coefficient of logarithmic work-hardening, the yield stress and the fracture stress of Cd-2 wt. %Zn alloy of different grain diameters and of Cd-17·4 wt. %Zn alloy decrease with increasing working temperature. Two relaxation temperature regions have been found, the low-temperature region of relaxation (below 483 K) and the high-temperature region (above 483 K). The fracture surface energy for Cd-2 wt. % Zn alloy has been calculated and found to be 1·2 J/m² at the two temperature regions of relaxation. X-ray investigations show that the residual internal strains in the deformed samples increase with increasing working temperature and exhibit a peak value at 483 K.     

Multiphase percolation and Josephson model for high-temperature superconductivity

A four-phase percolation problem is used to simulate the Josephson model for high-temperature superconductivity both as a four-phase and a three-phase system. We implement the method on an IBM PC microcomputer using PASCAL language.     

Hole burning in the optically detected zero-field spectrum using eedor

Using EEDOR, hole burning is demonstrated in the optically detected zero-field spectrum of tetrachlorobenzene in durene at 1.6°K, thus providing evidence that a large contributor to the width in these spectra is inhomogeneous broadening. Using phase sensitive detection in conjuction with EEDOR, a highly resolved optically detected microwave spectrum of a selected narrow distribution of molecules dissolved in a host is recorded. The potential use of this technique in eliminating inhomogeneous broadening from the phosphorescence-microwave double resonance spectrum is indicated.     

On the radical mechanism for photoinduced nucleation of alkane vapors

The addition of 10^?5 — 2 Torr of NO, a radical scavenger, is found to significantly quench the rate of photonucleation of nonane by NO₂ or CH₃I in a diffusion cloud chamber. This confirms a recently proposed radical mechanism for the photoinduced nucleation of these systems. The photonucleation rate of nonane induced by o-tolualdehyde (a system whose mechanism is not known) is similarly quenched by the addition of small amounts of NO, suggesting a radical mechanism. A mechanism for this system, based upon the formation of nonane radicals (resulting from hydrogen abstraction from nonane by the carbonyl molecules in the n,π* singlet or triplet state) followed by further reaction of the radicals to form low vapor pressure species, is discussed. Acetone, a system known to dissociate into radicals, is found to photoinduce nucleation of nonane when excited to the lowest singlet or triplet excited states. This adds further support to the proposed radical mechanism and suggests that acetone dissociates in its lowest singlet as well as its lowest triplet state. A theoretical model is outlined in which the production of large involatile alkanes (dimers and higher polymers) are formed from an initially produced nonane radical. These results are combined with binary nucleation theory in order to calculate the effect of these species on the rate of nucleation. These calculations indicate that low concentrations of these involatile species can indeed induce nucleation. The ability of small, photochemically produced polymers to induce nucleation is also examined and the time dependent space distribution of polymers (e.g., vinyl polymers) generated by chain transfer from a single free radical is derived. The small polymers formed in this process are analogous to the species formed in the photoinduced nucleation of alkane vapors.